Recent modelling performed at Simon Fraser University in Canada found that the zero-emission warming commitment – the rise in temperature following a cessation in carbon-dioxide emissions – could range from 0.2 to 0.9 °C for scenarios that involve a quadrupling of pre-industrial concentrations of carbon dioxide in the atmosphere.

This output will help determine whether carbon budgets need adjusting, and by how much, to satisfy future temperature targets. If global mean surface air temperature keeps rising once emissions cease, for example, then allowable cumulative emissions must be lowered to reach the same target.

Writing in Environmental Research Letters (ERL), the scientists described the commitment as a balance between the warming effect from declining ocean heat uptake and cooling associated with a drop in radiative forcing (as carbon is pulled out of the atmosphere into the land or sea). The former depends on how close the system is to a state of thermal equilibrium and the latter on how close the system is to bio-geochemical equilibrium, so the study focuses on both factors.

In all simulations, the researchers observed a positive warming commitment – an increase in global mean surface air temperature. The result implies that the warming effect of the decline in ocean heat uptake dominates.

The scientists added that the scenario prior to zeroed emissions has the strongest effect on the warming commitment – outweighing both the time of zeroed emissions and the time horizon over which the commitment is calculated. While the greatest impact is reported for a quadrupling of carbon-dioxide concentrations over pre-industrial levels, the team wants to examine a wide range of conditions.

"We're also interested in quantifying the zero-emissions warming commitment for low-emissions scenarios – for example, those corresponding to a temperature target of 1.5 °C," Dana Ehlert, who conducted the study together with Kirsten Zickfeld told environmentalresearchweb. "Preferably using a range of climate models."

Also, as the group acknowledges, there are other emissions to factor in alongside carbon dioxide, such as aerosols and short-lived greenhouse gases.

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